“We show that wherever there were good conditions for gerbils and fleas in central Asia, some years later the bacteria shows up in harbour cities in Europe and then spreads across the continent,” Prof Stenseth said.

He said that a wet spring followed by a warm summer would cause gerbil numbers to boom.

“Such conditions are good for gerbils. It means a high gerbil population across huge areas and that is good for the plague,” he added.

The fleas, which also do well in these conditions, would then jump to domestic animals or to humans.

And because this was a period when trade between the East and West was at a peak, the plague was most likely brought to Europe along the silk road, Prof Stenseth explained.

‘Perfect storm’

“To me this was rather surprising,” he said.

“Suddenly we could sort out a problem. Why did we have these waves of plagues in Europe?

“We originally thought it was due to rats and climatic changes in Europe, but now we know it goes back to Central Asia.”

The team now plans to analyse plague bacteria DNA taken from ancient skeletons across Europe.

If the genetic material shows a large amount of variation, it would suggest the team’s theory is correct.

Different waves of the plague coming from Asia would show more differences than a strain that emerged from a rat reservoir.

The plague died out in Europe after the 19th Century, however outbreaks continue to this day in other parts of the world.

The World Health Organization said there were nearly 800 cases reported worldwide in 2013, including 126 deaths.

In another paper, published in the American Journal of Tropical Medicine and Hygiene, researchers in the US said that the expansion of agriculture was placing East Africa at an increased risk of the plague.